Pneumocystis pneumonia (PCP) is a fungal disease associated with immunosuppressive conditions such as AIDS, cancer, rheumatic disease, organ transplant, malnutrition, etc. The biology of this fungus is poorly understood, research tools are limited and current treatments are inadequate. We demonstrated that Pneumocystis depends on its host for the critical biochemical intermediate S-adenosylmethionine (AdoMet), that PCP causes a reduction in host lung and plasma AdoMet, that systemic nicotine treatment to reduce lung AdoMet decreases vulnerability to PCP in an animal model, and that AdoMet infusion increases the intensity of animal model PCP. Our goal is to develop a new approach to PCP prophylaxis &treatment: limit the availability of AdoMet necessary for Pneumocystis growth. The first Aim is to resolve the biochemistry of lung-specific AdoMet depletion induced by systemic nicotine infusion;this information will help identify molecular targets for drug discovery research. We know nicotine induces polyamine catabolism in lungs, but we don't understand the differences in responses of other organs. We will compare biochemical responses of lung, liver and kidney of animals infused with nicotine by analyzing tissue explants prepared from nicotine-treated and control animals using a combination of metabolic flux and enzyme assay methods. We know that only some lung cells respond to nicotine with AdoMet reduction and our second Aim is to determine which cells respond;this information is needed to understand the response, to identify the nicotine target, and to develop an in vitro model needed for further drug development. We will isolate lung cell types for biochemical &proteomic analyses and examine lung sections for differences in metabolic enzyme expression. Our third aim is to determine the best metabolic targets for altering the supply of AdoMet for Pneumocystis: targets to decrease the supply thereby treating/preventing PCP. We will also determine the relative importance to Pneumocystis of AdoMet obtained from lungs and from the entire extracellular pool.